The amount of power that is allowed to be radiated is stipulated for many transmission systems, in particular in the field of mobile radio. This requirement imposed on the total radiated power (TRP) permits only slight deviations.
The high-frequency signals to be emitted are generally transmitted using lines which lead to a transmitting antenna, for example. If these lines are not terminated with the requisite line impedance, standing waves may propagate on them. In this case, a wave running on the line is reflected at the end of the line. The returning wave can then impair the wave running on the line. In the case of extreme mismatches, this may completely obliterate the wave running on the line. However, the extent to which the wave is obliterated also depends on the phase angle of the signal which is transmitted using the line and is intended to be emitted using an antenna, for example. Fluctuations in the radiated power may thus arise even if a constant power level has been set in a transmission path or an amplifier, for example. In order to make it possible to accurately set the power in a transmission path, the influence of the phenomena which obliterate signals which are intended to be emitted should be reduced and the voltage standing wave ratio (VSWR) should thus be improved.
One approach to this is to use a special power amplifier having a split signal path. The power of a high-frequency signal which is intended to be emitted could be split into two signal parts using a hybrid coupler. One part of the signal can be amplified by a respective amplifier without a phase shift, and a second part of the signal can be amplified by a respective amplifier after having been phase-shifted through 90° by the hybrid coupler. The power of the amplified signals is combined by a further hybrid coupler and is output to an antenna in the form of a transmission signal. However, the hybrid couplers in the power amplifier require a relatively large amount of space and, in addition, have an attenuating behavior which can be compensated for only by means of a higher gain and thus a greater amount of requisite power.